Vehicles with an Internal Combustion Engine (ICE) include an exhaust gas treatment system for treating the exhaust gas from the engine. The configuration of the treatment system depends, in part, upon whether the engine is a diesel engine (which typically operates with lean burn combustion and contains high concentrations of oxygen in the exhaust gases at all operating conditions) or a stoichiometric spark-ignited engine (which operates at a nearly stoichiometric air-to-fuel (A/F) ratio). The treatment system for the diesel engine includes a diesel oxidation catalyst (DOC), which is capable of oxidizing carbon monoxide (CO) and hydrocarbons (HC). The treatment system for the stoichiometric spark-ignited engine includes a three-way catalyst (TWC), which operates on the principle of non-selective catalytic reduction of NOx by CO and HC.